Medical implants or prostheses function to replace or augment various structures and tissues in the body. Medical implants include, for example, intervertebral disc replacement devices, spinal fixation systems, facet arthroplasty devices, artificial hips, bone screws, bone plates and rods, prosthetic knee replacements, arterial stents, pacemakers, heart valves, artificial hearts, artificial sphincters, etc. The effectiveness of medical implants sometimes is highly dependent upon the implant's interactions with surrounding tissues. For example, in the case of bone implants, it may be desirable that tissue attachment from adjacent bony structures occur at the bone implant's surface in order to integrate the bone implant with the rest of the skeletal system.
In a biological system, several elements are primordial for survival. The dissection of the different elements of biological systems is translated in tissue engineering by three general ingredients; the cells, biological active factors such as growth factors or growth factor antagonists and scaffolds. The cells (I) are extracted from a donor, who is the patient himself, another person, preferably a close relative of the patient (preferably having the same germ lines) or an animal (autogenic, allogenic and xenogenic transplantation, respectively). The cells can either be a stem cell, a tissue progenitor cells or a differentiated tissue specific cell; the biological active factors (II) attract tissue forming cells at the site of implantation, and/or promote cell adhesion, stimulate proliferation, and guide differentiation of progenitor cells in the desired cell type to reconstitute a functional tissue; the scaffolds (III) are made of a biocompatible material being either synthetic or natural in origin. The scaffold creates the optimal microenvironment in which the various cell types can mature into a functional tissue. Maturation of the constructs can occur in vitro or in vivo after implantation of the scaffold at the desired location in the body. The integration/interaction of these elements leads to the creation of new tissues.
Cell life depends on chemical interactions and reactions, which are extremely well coordinated in time and space and are under the influence of genetic instructions as well as the environment. The aim of a scaffold material, selected for a tissue engineering application, is to create an optimal microenvironment for de novo tissue formation for example by mimicking the natural extracellular matrix (ECM). The ECM is a net of secreted products that surround and support cells in tissue. The ECM consists of a mixture of structural and functional molecules organized in a three-dimensional structure that is specific for each tissue type. Most of these molecules are well known; they form a complex mixture of proteins and polysaccharides. The ECM functions as a reservoir of bioactive molecules such as growth factors and growth factor antagonists. The bioactive molecules that reside in the ECM and their spatial distribution provide a cocktail of biological signals. The balance in activation of biological processes by arrays of growth factors and the inhibition of their activity by respective antagonists determines all biological response such as cell proliferation, cell differentiation, cell maturation, cell death and the formation of a functional organ. The ECM is a reservoir for growth factors and antagonists. Since cellular functions are regulated by cell-cell communication, cell-substratum interactions, and soluble factors, it is of prior importance to select an adequate biomaterial, and select an adequate set of growth factors and/or growth factor antagonists to incorporate in the scaffold for optimal tissue formation. Each tissue requires its own set of conditions. Viewing the biomaterials as units to interact with biological systems rather than inert substances, innovative designs in the field of biomaterials are needed to optimize the constructs for functional tissue formation.
The adsorption/incorporation of proteins onto/into biomaterials can influence material properties and degradation. The kind of interactions between proteins and an implant is determined by the properties of both (e.g. size, charge, structural stability, topography or chemical composition).
There is a need for a method that more fully regulates the interactions between medical implants and surrounding tissues and that discourages disadvantageous interactions of medical implants and surrounding tissues. Additionally, there is a need for a method to guide tissue attachment to medical implants. There also is a need for a method that stimulates advantageous interactions of medical implants and surrounding tissues.
The challenge faced by researchers in the field is to make implants with improved properties such as better attachment to the surrounding tissue, improved growth, differentiation and migration of cells responsible for wound healing. It is therefore an object of the present invention to substantially overcome or ameliorate one or more disadvantages of the prior art.